This invention relates to indazoles of value in therapy. U.S. Pat. No. 3,988,347 describes a process for the preparation of indazoles substituted at one or more of the 4-, 5-, 6- and 7-positions which are indicated to be useful as intermediates in the preparation of preservatives, dyestuffs and pharmaceuticals. U.S. Pat. No. 3,817,714 describes 1-substituted indazoles which are preparable from the compounds of U.S. Pat. No. 3,988,347 and which are useful for preserving aqueous compositions that are subject to decomposition and spoilage by the action of bacteria, for example latex paints. U.S. Pat. No. 3,817,714 further describes the possibility of using 1-unsubstituted indazoles as preservatives For aqueous compositions in the non-therapeutic contexts described in that patent.
The compound L-N.sup.G -nitroarginine methyl ester has been described (Moore et al., British Journal of Pharmacology, 1991, 102,198-202) as blocking the enzyme nitric oxide synthase but is of little value as a therapeutic agent since it blocks this enzyme not only in the brain but also peripherally. We have now found that certain indazoles also block nitric oxide synthase and have the very particular advantage of being selective for the enzyme in the brain and elsewhere in the central nervous system.